Field of the Invention
The invention relates to ventilation apparatuses, and more particularly to ventilation apparatuses that can provide functions of air discharge without use of electric power.
Description of the Related Art
Generally, there are two types of conventional ventilation apparatuses disposed on the rooftops of houses. One conventional ventilation apparatus is operated by electric power and is provided with an electric fan. Air can be expelled from a building by the electric fan. Accordingly, operation of this conventional ventilation apparatus consumes electric power.
The other conventional ventilation apparatus is operated without use of the electric power. Specifically, a spherical drainage fan is disposed on the top of the conventional ventilation apparatus. Based upon the principle of hot-air rising, indoor hot air rises to the top of the building. Then, the indoor hot air drives the spherical drainage fan to rotate and is expelled thereby. Nevertheless, the spherical drainage fan cannot rapidly expel the indoor hot air. Here, the spherical drainage fan is mainly used to expel rainwater by centrifugal force generated by the rotation thereof, thereby preventing the rainwater from entering the building. As the other conventional ventilation apparatus is operated only by the principle of hot-air rising, an expellant speed for the indoor hot air may be very slow if only a minor temperature difference exists between the interior and exterior of the building.